Superregenerative receiver circuit



NOV. 5, 1946. J: WORCESTER, JR 2,410,768

SUPER-REGENERATIVE RECEIVER CIRCUIT Filed Feb. :5, 1945 l I I i Z I I5 /2 27 I I0 25 '29 I7 I [a 28 FILTER L .Eg=0 B 52 R 5 =1 Caron-" .9 P \A (II/v1 Inventor:

Joseph Patented Nov. 5, 1946 UNITED STATES SUPERREGENERATIVE RECEIVER CIRCUIT Joseph A. Vvorcester, J12, Fairfield, Conn, assignor to General Electric Company, a corporation of New York Application February 3, 1943, Serial No. 474,501

8 Claims. 1

My invention relates to super-regenerative receiver circuits and it has for its object to provide an improved super-regenerative receiver circuit which is particularly adapted for receiving super-audible frequencies such as pulses and television signals.

A super-regenerative receiver of the usual type is essentially similar to an ordinary regenerative type of receiver but has additionally a local source of super-audible oscillations which are introduced-into the detector circuit of the receiver in a manner to vary the deteotors operating point at a uniform rate. This local oscillation, known as the quench or interruption oscillation, allows the superregenerative detector to oscillate at the carrier frequency, in the manner of the ordinary regenerative detector circuit, only when the varying operating point is in a region suitable for the production of oscillations, The constant interruption of oscillations in the detector circuit by the quench oscillations permits amplification of the signal in the detector to very large proportions. Similar results are obtained in an ordinary regenerative circuit when regeneration at the signal frequency is carried to the point that the detector circuit begins to oscillate at a low frequency simultaneously with its oscillation at the signal frequency. Such a low frequency oscillation has the same effect as the quench oscillation pro- 30 duced by a separate source of oscillation, and a circuit so. operating is'custQmariL referred to as to serve as an auxiliary feed-back means to ina self-quenching super-regenerative detec or 01 with 'nitude of local oscillations.

cuit. In such a circuit the repetition rate or quench frequency, which iscontrolled by the 35 time constant of the grid-cathode circuit of the detector, determines the maximum modulation frequency that can be reproduced by the receiver circuits.

Accordingly, it is anobject of my invention to provide a self-quenching super-regenerative circuit in which the signal frequency oscillations of the receiver circuits are interrupted at a very rapid rate, thereby permittingv the reproduction of pulse modulations of very short duration.

Another object of m-yinvention is to provide an auxiliary discharge path for the grid of a super-regenerative detector which path is operative only during negative half cycles of quench oscillations to decrease the duration of such negative half cycles.

The features of my invention which I believe to be novel are' set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 represents certain portions of a receiver circuit embodying my invention; and Figs. 2 and 3 illustrate certain operating characteristics of the circuit of Fig. 1.

Referring to Fig. 1, I have shown an electron discharge device Ii] having radio frequency input circuit H and an oscillatory circuit lZresonan-t at the radio frequency. Modulating signals appearing in the output of the device m are supplied to subsequent stages of the receiver over conductor !3. The device Ill operates as a selfquenching super-regenerative detector and the control circuit I4 is provided to increase the interruption rate of the super-regenerative circuit.

The electron discharge device It is shown as a triode having an anode l5, a cathode l6 and a control electrode H. The cathode i6 is heated by means of a filament [8, power for heating the filament l8 being supplied thereto over conductor H! from anyv suitable source through inductance 20 acting as a filament choke. Inductance 2| serves as a second filament choke connected between the opposite terminal of filament l8 and ground. By-pass capacitors 22 and 23 are connected between the respective terminals of the filament l8 and cathode it. An inductance coil 26 is connected between cathode is and ground The oscillatory circuit connec e etween anode l5 control electrode l'l comprises a pair of parallel conductors, or rods, 21 and 28 which function as a transmission line having. a length approximately equal to a quarter wave length at the tuned radio frequency and capacitor 29 is provided across the outer extremitiesof this line to function as means for short-circuiting or closing the end of the line at radio frequency. g

The radio frequency input circuit l i may comprise the concentric transmission line 24 having its inner and outer conductors connected at their upper ends to a suitable antenna (not shown) and at their lower ends to the coupling loop 25 lying between the parallel rods 2'? and 28. The outer conductor of line 24 is grounded at its lowermost point 24'.

Operating potential for the anode it may be supplied from any suitable source, such as the battery, 39, through local resistor 35, across which audio frequency voltages are developed,

and filter 32, provided to remove radio frequency and quench frequency voltages from the output conductor I3.

Resistors 34 and 35 are connected between the outer end of conductor 28 and ground to function as the usual grid leak for the detector Hi. The point of connection 33 of resistor 34 with conductor 28 is shown as coupled to ground through a grid capacitance 31. This grid capacitance comprises the distributed capacity of the grid rod 28 and its associated wiring to ground.

The action of a radio receiver using superregeneration is, in general, quite complicated, especially when receiving super-audible oscillations. The fundamental principle of super-regeneration, however, is based on the impression of a low frequency variation, usually called quench action which periodically changes the operating point of an electron discharge device in an oscillatory circuit. Such periodic change may be accomplished by varying either the anode voltage or the grid bias voltage of the device.

The arrangement of Fig. 1 utilizes the grid bias method of introducing the quench voltage into the detector circuit and in the operation of the portions of the receiver circuit thus far described, the electron discharge device in operates in the usual manner to amplify signals supplied to the control electrode i! from the radio frequency input circuit. The oscillatory circuit I2 connected between the anode and control electrode is adjusted to resonance at the frequency of the input signals. Since each of the conductors of this line has a length equal efiectively to a quarter of a wave length of the received oscillations, oscillations from the anode l5 are shifted through 180 in traveling between anode l5 and control electrode I! in this resonant circuit and, hence, these signals are supplied to the control electrode as an input voltage which is in exactly the right phase to build uposcillations in the resonant circuit. The amplitude of these oscillations increases with each cycle until they reach an intensity sufiicient to provide a positivevoltage on flow in the circuit between grid I! and cathode l6 and comprising resistors and 34 and rod 28. .Current flow through the grid leak resistors 34 and 35 provides a negative voltage for control electrode l1, biasing this electrode considerably beyond the plate current cutoff point. Hence,

oscillations cease when this action occurs, the V capacitance 3'Lserving to maintain a high negan c electrode H. The negative charge on capacitance 31 graua through resistors 34 and 35 until plate current again begins to flow in device In and the cycle is repeated.

The operation of this portion of the circuit of Fig. 1 may be illustrated withgreater clarity by reference to Fig. 2 in which the reference line 53 represents the voltage Eg ofcontrol electrode H at which conduction of anode current in device Ill is .cut oif and reference line 51 represents zero potential for control electrode ii, that is, the

' potential at which grid current flow in device I0 is started.' Curve 52 illustrates the manner in which oscillations build up in the tuned circuit l2, starting with zero value at point A and gradually increasing in amplitude until, at point B, control electrode l1 reaches a positive potential and grid current flows in device it). When such grid current flows, the potential of control electrode i1 is rapidly reduced to the value C, which value is considerably below the plate current cut control electrode l I and cause grid current 70 ground "an ofi designated by line 50, and oscillations must necessarily cease when electrode I1 is driven to such a negative value. At the same time capacitance 31 is charged to this high negative voltage. The high negative charge on capacitance 37 gradually leaks off through resistors 34 and 35 at an exponential rate, as indicated by the portion of the curve CD, until plate current again begins to flow in tube It and the cycle is repeated.

The repetition rate, or frequency, of the quench oscillations operates to limit the maximum modulation frequency that can be reproduced in the output circuits of the receiver. This repetition rate is controlled primarily by the portion of the curve CD, that is, the time required for the high negative charge to be removed from the capacitance 31. The frequency of the quench oscillations limits the modulation frequency because it is necessary to filter the quench frequency from the output circuits and such filtering can be accomplished Without adversely affecting desiredmodulation signals, only by making the repetition rate high compared with the highest modulating frequency to be reproduced.

The repetition rate of the quench oscillations in the portion of the receiver circuits thus far described is controlled largely by the capacitance 31 between grid H and ground. To increase the rate to its maximum value, this capacitance is reduced to as low a value as possible, the ultimate in this direction being reached when the value of capacitance 31 is reduced to the input stray capacity between grid H and rod 28 and ground. The repetition rate may also be increased somewhat by decreasing the value of grid leak re sisters 34 and 35. The value of these resistances must be maintained sufficiently large, however, that oscillations in the oscillatory circuit 12 are not clamped to the point that super-regeneration is prevented.

In order to permit further increase of the repetition rate of the quench oscillations, in accordance with my invention; control circuit I4 is provided for the receiver circuits thus far described.

This circuit comprises an electron discharge device 40 having its anode 4| connected to the posi tive terminal of the potential source 38, its control electrode 42 connected to ground and its cathode 43 connected to the common point of resistances 34 and 35 by means of conductor 44. The combined stray capacity of conductor 44 to the cathode device!!!) are represented by capacitance 45.

In the control circuit l4, since the cathode 43 onnected to ground through resistor 35 while control e 2 is connected directly to ground, the device 40 is nor I 2 -conducting and essentially removed from the circuit of super-regenerative detector In during the time that oscillations are building up in the resonant circuit l2. Resistor 3'4 is quite small compared to resistor 35, the latter preferably being of the order of 1 megohm. When the amplitude of the oscillations in the oscillatory circuit i2 is sufficient to cause current to flow between grid l1 and cathode is, tending to bias the oscillator tube l3 beyond cutofi by the potential drop across resistor 35, this negative bias is also applied to the cathode of device 40. Since the control electrode 42 is grounded, the negative bias of cathode 43 causes control electrode 42 to become positive with respect to the cathode and the positive voltage applied to anode 4| produces anode current in device 40. This anode current flows through resistor 35 in a direction opposite to that of the grid current in device In. and is effective to remove rapidly the negative charge accumulated on the oscillator grid IT.

The operation of this portion of the circuit of Fig. 1 is illustrated in Fig. 3 in which reference lines 50 and 5| represent the values of gridvoltage pointed out previously. The curve 52 illustrates the manner in which oscillations build up in the tuned circuit l2, starting with zero value at point A and gradually increasing in amplitude until, at point B, the amplitude is such that control electrode ll becomes positive and grid current flows inv device It; As stated previously, when such grid current flows, the potential of control electrode I1 is reduced to the value C, which value is below the plate current cutoif point.

When control electrode I! is driven to the potential 0' below the plate current cutoff value of tube Ill, current flows in device 40 and the a negative charge accumulated on capacitances 3'! and 45 is rapidly removed by the current flow in tube 4c. The amount of negative bias, that is, the potential C to which grid I! is driven before conduction in tube 40 is started, may be controlled by adjusting the time constant of resistor 34 and capacitance 45. The recovery time of the grid circuit and, hence, the repetition rate of the quench oscillations are controlled by the time constant of resistors 34 and 35 and capacitances 31 and 45.

The electron discharge device 40, therefore, acts as an auxiliary discharge path for the grid I1 of the super-regenerative detector. This path is operative only during negative half cycles of quench oscillations and provides means for decreasing the duration of such negative half cycles. In the usual type of super-rengerative receiver circuit, a quench. frequency of between 30 and 80 kilocycles is obtainable. By the addition of the control circuit I4 and proper adjustment of the values of resistances 34 and 35 and by maintaining capacitances 3'1 and 45 at a minimum, repetition rates as high as 1000 kilocycles may be obtained. By using quench oscillations of such high frequencies, this type of receiver may be employed in pulse signalling systems and the quench oscillations may be removed from the output circuit without disturbing signals of the pulse frequency.

While I have shown a particular embodiment of my invention, it is apparent that various modifications may be made. Thus, the quench frequency may be controlled by the application of suitable bias to grid 42 of electron discharge de- .7 Vice 4!]. It will be understood, therefore, that I do not wish to be limited to the embodiment shown since various modifications may be made, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim 'as imn ddesire tosecur Letters Patent of the United States is;

1. A detector cilgzuit for signal modulated carrier waves comprising an electron discharge device having an anode, a cathode and a control electrode, an input circuit for said device connected between said cathode and said control electrode, an output circuit for said device connected between said anode and said cathode, a tuned circuit resonant at the frequency of said waves and connected to couple said input and output circuits, means including a resistor connected between said cathode and said control electrode for periodically rendering said discharge device non-conductive, and means including a unilateral. conducting device connected across at least a portion of said resistor for controlling the duration of the non-conductive intervals.

2. In an ultra high frequency super-regenerative receiver, the combination of an electron discharge device comprising an anode, a cathode, and a control electrode, a signal input circuit connected between said control electrode and cathode, an output circuit connected between said anode and cathode, a tuned circuit connected to couple said input and output circuits thereby to produce oscillations in said discharge device, an impedance connected between said control electrode and cathode and including a capacitive element arranged periodically to be charged by current flowing therethrough, said capacitive element being disposed when charged to bias said discharge device to cutoff thereby periodically to interrupt said oscillations, and means including a second electron discharge device responsive to said cutoff bias and connected across said impedance for controlling the rate of 1 5 interruption of said oscillations.

3. In an ultra high frequency self-quenching super-regenerative receiver, the combination of an electron discharge device comprising an anode, a cathode, and a control electrode, a signal input circuit connected between said control electrode and cathode, an output circuit connected between said anode and cathode, a tuned circuit connected to couple said output and input circuits thereby to build up oscillations in said output circuit, a resistance and a capacitive element connected in parallel circuit relation between said control electrode and cathode to conduct current upon the attainment of a predetermined intensity of said oscillations, said current charging said capacitive element to bias said discharge device to cutoff and to interrupt said oscillations, and means comprising a second electron discharge device having a pair of electrodes connected across at least a portion of said resistance for controlling the rate of discharge of said capacitive element thereby to control the periodicity of said interruptions.

4. An ultra high frequency self-quenching super-regenerative receiver circuit comprising a source of signal waves, an electron discharge device having an anode, a cathode, anda control electrode, an input circuit for said discharge device connected between said cathode and said control electrode, an output circuit for said device connected between said anode and said cathode, a tuned circuit resonant at the frequency of said signal waves and connected to couple said input and output circuits to build up oscillations in said to output circuit, a resistance and a condenser connected in parallel circuit relation between said 0 e co rodeand said cathode, oscillations in said output circuit being periodically interrupted by the flow of grid current through said resistance and charging of said capacitor when said oscillations attain a predetermined intensity thereby to bias said discharge device to cutoif, and means for rapidly removing said biasing potential including a second electron discharge device having a control electrode cathode circuit connected across at least a portion of said resistance, said second device being non-conductive when said first device is producing oscillations in said resonant line and being rendered conductive by said biasing potential to produce current flow to the flow of said grid current.

5. A self-quenching super-regenerative receiver circuit comprising a source of signal waves,

an electron discharge device having an anode, a cathode and a control electrode, an input circuit for said device connected between said cathode and said control electrode, an output circuit for said device connected between said anode and said cathode, a tuned circuit resonant at the frequency of said waves and connected to couple said input and said output circuits thereby to build up oscillations in said output circuit, means interposed between said cathode and said control electrode and responsive to the intensity of said oscillations for periodically interrupting said oscillations, and means including a unidirectional conducting device associated with saidinterrupting means for controlling the periodicity of said interruptions.

6. A detector circuit for signal modulated carrier waves comprising an electron discharge device having an anode, a cathode and a control electrode, an input circuit for said device connected between said cathode and said control electrode, an output circuit for said device connected between said anode and said cathode, a tuned circuit resonant at the frequency of said waves and connected to couple said input and output circuits, means including a capacitive element between said cathode and said control electrode arranged to be charged by current flowing through said device and periodically to render said discharge device non-conductive, and means including a unilateral conducting device connected to control the rate of discharge of said condenser thereby to control the duration of the non-conductive intervals.

'7. A detector circuit for signal modulated car- -through said resistance in a direction opposite rier waves comprising an electron discharge device having an anode, a cathode and a control electrode, an input circuit for said device connected between said cathode and said control electrode, an output circuit for said device connected between said anode and said cathode, a tuned circuit resonant at the frequency of said waves and connected to couple said input and output circuits, capacitive means connected between said cathode and control electrode for periodically rendering said discharge device nonconductive, and means including a source of unidirectional potential and a second electric discharge device connected to control the rate of discharge of said capacitive means thereby to control the duration of the non-conductive in tervals.

8. A detector circuit for signal modulated carrier waves comprising an electron discharge device having an anode, a cathode and a control electrode, an input circuit for said device connected between said cathode and said control electrode, an output circuit for said device connected between said anode and said cathode, a tuned circuit resonant at the frequency of said waves and connected to couple said input and output circuits thereby to build up oscillations in said discharge device, means for periodically interrupting said oscillations including a capacitive element connected between said cathode and said control electrode and arranged by its charge to bias said discharge device to cutoff when said oscillations attain a predetermined intensity, and 'means including a unilateral conducting device rendered conductive only upon charging of said capacitive element to increase the rate of dissipation of said charge.

JOSEPH A. WORCESTER, J R. 

